The following processes are generally employed for treatment of waste water containing dioxins, for example, for treatment of leachate from a general waste final disposal site and for treatment of industrial waste water such as pulp mill waste water.
The process for the treatment of leachate from a landfill includes the steps of: removing dirt, sand and the like in a pretreatment plant; removing heavy metals such as calcium and manganese by coagulation and sedimentation thereof in a calcium removal plant; removing BOD substances (BOD) and nitrogen-containing substances (T-N) by biodegradation thereof in a biological treatment plant; removing COD substances (COD), floating matters, phosphorus-containing substances (T-P) and the like by coagulation and sedimentation thereof in a coagulation/sedimentation plant; removing fine floating matters in a sand filtration tower; removing dioxins remaining in the leachate in an activated carbon adsorption column after treatment in an ozone/ultraviolet reactor; and releasing the resulting leachate.
Sludge produced in the calcium removal plant, the biological treatment plant, the coagulation/sedimentation plant and the like is thickened in a sludge thickener, and then stored in a sludge storage tank. Thereafter, a dewatering promoter is added to the sludge, which is in turn dewatered by means of a sludge dewatering machine. The dewatered sludge cake is again disposed of in a landfill of the final disposal site.
However, a major proportion of dioxins are incorporated in the sludge produced in the calcium removal plant, the biological treatment plant, the coagulation/sedimentation plant and the like. Therefore, if the dewatered sludge cake is disposed of in the landfill, dioxins are accumulated in the landfill of the final disposal site, and again leached out into leachate. As a result, the decomposition and removal of dioxins requires a longer period of time.
In order to solve the aforesaid problem, it is an object of the present invention to provide a process for decomposition and removal of dioxins contained in sludge.